Simulated smoke is generated for a number of applications, including military screening of areas, theatrical effects, and training of fire fighters, among others. The present invention relates to these usual applications for simulated smoke generation, but it is particularly applicable to those applications where the generation of the simulated smoke must be closely controlled. As an example thereof, when simulated smoke is used for training fire fighters, the training environment is arranged such that when the trainee properly applies the correct extinguishing agent, at the correct position of a simulated fire and for the correct length of time, the simulated fire is extinguished, and the simulated smoke associated therewith is likewise extinguished. On the other hand, for example, if the trainee does not apply the extinguishing agent for the correct length of time, even though the simulated fire and smoke are discontinued, a "flashback" or "burnback" of sudden reignition is simulated by an immediate burst of simulated fire and smoke. Thus, as opposed to other applications, such as theatrical applications, where the commencement and discontinuance of the smoke in very short periods of time is not necessary, for purposes of training fire fighters, such commencement and discontinuance in a very short period of time is most desirable, in order to realistically represent actual fire conditions for the trainee.
Simulated smoke generation is usually achieved by vaporizing a smoke-generating fluid and mixing that vaporized fluid with air such that an aerosol fog of the vaporized and at least partially condensed smoke-generating fluid is produced. As can be appreciated, therefore, in order to generate such a simulated smoke from a smoke-generating fluid, the apparatus and methods utilized must heat the smoke fluid to a temperature sufficient to cause substantial vaporization thereof and, at the same time, mix the vaporized smoke fluid with air to provide the aerosol fog of the vaporized and condensed smoke fluid. However, as can also be appreciated, heating the smoke fluid to temperatures sufficient to cause substantial vaporization for smoke-generating purposes and then cooling that fluid to temperatures such that substantial generation of vapor and smoke does not occur, in a very short period of time, poses a considerable difficulty in the art.
Basically, in the prior art, simulated smoke has been produced in one of several manners. First, a hot gas, usually air, is passed in contact with smoke fluid, which may be in either a heated or unheated condition. The hot air causes vaporization of the smoke fluid into the air, and, with cooling, the desired fog results. However, as can be appreciated, if the hot air is used to heat the smoke fluid, a considerable time lapse is required for enough hot air to pass in contact with the smoke fluid to cause sufficient heating of the fluid and generation of vapors therefrom. Therefore, there is a slow and gradual buildup of vaporized smoke fluid in the hot air, and, as a result, there is, correspondingly, a slow and gradual buildup of the fog so produced. This, of course, would be most unsatisfactory for fire fighter trainees, since this would not duplicate actual fire fighting experiences.
Another method is that of heating a pool of smoke fluid to a temperature sufficient that substantial vapors therefrom are produced, and then blowing air, heated or unheated, over the fluid to cause the desired fog of simulating smoke. However, as can be appreciated, in this method, again, during the time period required to sufficiently heat the pool of smoke fluid and the time period required for cooling the pool of smoke fluid, the density of the fog produced will slowly increase and then slowly decrease, respectively, which, again, is not a realistic representation of actual fire fighting conditions.
Another method in the art is that of atomizing the smoke fluid and forming an aerosol thereof directly in the forced air, which may or may not be heated. However, the fog produced by this method, being relatively cold, has a density greater than air, and rather than the fog rising, for example in a room, so as to simulate the actual effect of smoke, the fog settles toward the floor of that room and gives the appearance of a theatrical effect, rather than a fire effect. This, of course, is totally unacceptable for training fire fighters.
Another method in the art admixes steam with the smoke fluid to produce vapors thereof, and then forces that mixture through narrow orifices into the atmosphere where the steam and vapor are chilled to produce a fog. Here again, the rising effect of smoke in actual fires is not duplicated.
Conventional smoke bombs have also been used for this purpose, but they are not controllable, since once the bomb is exploded, it continues to produce smoke, unabated, until the smoke fluid is depleted.
Representative of the above briefly discussed prior art are U.S. Pat. Nos. 4,439,341; 4,547,656; 4,568,820; 4,764,660; and 4,818,843.
Recently, it has been proposed in the art to provide a vaporizing unit for the smoke fluid where the smoke fluid passes between interior walls of a vaporizing chamber and exterior walls of a vaporizing element, where the passageway therebetween is narrow and produces a very high surface area/volume ratio. By this means, smoke fluid can be rapidly heated to produce vapors thereof, and then those vapors are expelled into the atmosphere for producing the desired fog (see U.S. Pat. No. 4,871,115). However, this apparatus has several distinct disadvantages. Firstly, there is a considerable thermal lag in heating and cooling the apparatus, with a corresponding lag in the commencement and discontinuance of smoke. Secondly, the narrow passage between the interior walls of the chamber and the exterior walls of the vaporizing element can be clogged by residues and thermal degradation products of the smoke fluid when heated to vaporization temperatures. This cause unevenness and discontinuities in the vapors produced and, hence, in the fog produced. Further, the fog is produced by passing the heated vapors to ambient air, for cooling and fogging purposes, and that fog, of course, as explained above, will be more dense than air and will, therefore, settle. This device is, therefore, very useful for producing theatrical effects, but is not particularly useful for fire fighter training.
It would, therefore, be of substantial advantage in the art to provide an apparatus and method for controllably generating simulated smoke, where that simulated smoke has the same rising characteristics as actual smoke and where that simulated smoke can be quickly commenced and quickly discontinued. It would be a further advantage in the art to provide for such smoke generation by use of relatively modern smoke fluids which have less toxicity and less potential for ignition than older smoke-generating fluids.